It is conventional to mount a rotary switch on the transmission housing externally thereof to receive mechanical gear selection inputs from the driver through linkages and output gear selections to a decoder module and the transmission electronic control unit via electronic signals. The switch includes a quadrant with a selected number of copper contact segments disposed thereon with each segment providing an output to the decoder module. The manual valve is mechanically coupled to a plate having indexing detents pivotably mounted on a shaft. The shaft extends through the transmission housing wall and a switch bar is fixedly attached to the shaft so that when a driver selects a gear, the switch bar moves across the quadrant to a predetermined position to contact one of the copper contact segments. The electronic control may monitor the gear position along with other inputs relating to such things as throttle position, output shaft speed, engine speed, engine load and so on.
Although this switch system is in wide use it suffers from certain limitations and disadvantages. For example, locating the switch outside the transmission housing removed from the manual valve results in an undesirable tolerance build up involving all the linking elements. Further, the switch is locating in a splash zone, particularly when used with four wheel drives, necessitating the provision of sealing means to prevent entry of water. The extra cost for such sealing means including venting rubes and the like adds significantly to the cost of the system.
It is therefore an object of the present invention to provide a reliable, low cost manual valve position indicator that is free of the above disadvantages of the prior art switch system mounted exteriorly of the transmission housing. Another object is the provision of a position indicator which also generates additional information for the electronic controller, particularly relating to when sufficient pressure has been applied to specific hydraulic circuits indicating if clutches are capable of transmitting engine torque.